Recent years have seen an online demand traffic parameter information service system via mobile phone connections in a field of vehicle-mounted navigation.
When a user which uses a navigation device sets his or her destination in a state which his or her own mobile phone is connected to this system, the navigation device is connected to a server at a parameter information center and starts destination guidance. This system also provides a service for update of maps, traffic congestion prediction, and a service of working hand-in-hand with Web (World Wide Web) sites on the Internet, and the user can enjoy these services.
By the way, a conventional navigation device that, in a communication system with which a mobile phone as mentioned above can connect, judges a call enable area and a call disable area which were informed to the navigation device in advance is known (refer to, for example, patent references 1, 2, and 3). More specifically, the navigation device matches call area parameter information with the field intensity at the vehicle position and judges whether the navigation device can make a phone call in the area, thereby being able to judge whether the navigation device can make a phone call in advance.    [Patent reference 1] JP,2000-295652,A    [Patent reference 2] JP,2006-157746,A    [Patent reference 3] JP,10-89984,A
However, although the technologies disclosed by above-mentioned patent references 1, 2, and 3 are effective in that the user can judge whether the navigation device can make a phone call in the area, either of them goes no further than matching the call area parameter information with the field intensity to judge whether the navigation device can make a phone call in the area, and does not take actual phone call conditions, e.g., a network traffic congestion condition into consideration.
Therefore, switching to a communication method in the area or useless communications occur, and this results in a load of an operation of handling communications for the switching or the useless communications being imposed on the user. Furthermore, because it is assumed that the mobile phone which the user uses can certainly establish a connection with the navigation device, in a case in which the mobile phone does not support the connection commands of the navigation device, the user simply cannot use the mobile phone to operate the navigation device or has to perform an operation of updating the software of the navigation device.
The present invention is made in order to solve the above-mentioned problems, and it is therefore an object of the present invention to provide a navigation device and an adaptively-controlled communication system that can reduce the load imposed on the user and carry out communications while preventing useless communications from occurring.